Inkjet type printers typically employ a print cartridge that is moved in a transverse fashion across a print medium. A current disposable inkjet print cartridge typically includes a self-contained ink container, a print head supporting a plurality of inkjet nozzles in combination with the ink container, and a plurality of external electrical contacts for connecting the inkjet nozzles to driver circuitry in the printer. Failure of a disposable print cartridge is usually related to the failure of the individual resistors used to heat the ink in proximity to each nozzle. However, as the inkjet technology has advanced, the reliability of the print cartridges has improved over the years dramatically. Current print head assemblies used in the disposable inkjet print cartridges are fully operable to their original print quality specifications after printing tens or even hundreds of times the amount of ink contained in the self-contained ink container. It is, therefore, desirable to extend the life of a print cartridge to take advantage of the long life of the print head assembly. Merely making the print cartridge container larger in size is not a satisfactory solution. The print cartridges are typically mounted on the moving carriage of the inkjet printer. However, the larger the volume of ink in the print cartridge, the greater the mass to be moved by the printer carriage. The greater mass places a greater burden on the motor that drives the carriage as well as the structure of the carriage itself. Printer performance will also be limited by a heavier carriage because of the increased inertia associated with a larger carriage. That inertia must be overcome at the two endpoints of the carriage motion. At these locations, the carriage reverses direction to begin another pass over the media during the printing process. Increased carriage inertia increases the time required to reverse direction for a given driving motor size and, therefore, can reduce print speed.
Japan Patent No. 2929804, filed on Oct. 5, 1991, discloses an on-carriage print cartridge that, in one embodiment, includes a porous ink-absorbent, such as a sponge, and a print head mounted in a vertical orientation at one side of the print cartridge. The print cartridge is refillable by vertically lowering an ink supply into a nest in the print cartridge. Ink conduit needles protruding from the bottom of the nest pierce a septum at the bottom of the ink supply. This enables the ink to flow from the ink supply to the porous ink-absorbent via a capillary channel in the print cartridge. Since the porous ink-absorbent appears to be internally sealed in the print cartridge, it cannot be cleaned or replaced. The ink supply can be made small enough to avoid too much weight on the carriage, but it results in frequent replacement of the ink supply. Moreover, because of the frequency that small ink supplies are spent, some method of detection of the ink level in the print cartridge is preferred to detect when the cartridge is out of ink.
U.S. Pat. No. 5,686,947 to Murray et al., discloses a wide format inkjet printer that provides a substantially continuous supply of ink to a print cartridge from a large, refillable ink reservoir mounted within the inkjet printer. Flexible tubing, permanently mounted within the inkjet printer, connects the reservoir to the print head. The off-carriage ink supply allows a print cartridge to print in the printer for the full cartridge life while eliminating the problems related to the extra weight on the carriage of an on-carriage large ink system.
It should be understood, however, that the continuous replenishment of the ink container within a disposable inkjet print cartridge may bear some undesirable consequences, i.e., a larger ink pressure variation inside the print cartridge. It therefore becomes important to reduce ink pressure variation inside the print cartridge in order to achieve the best image quality. A variety of factors may induce ink pressure variation inside the print cartridge. For example, a change in the ink level in the refillable ink reservoir is directly related to the ink pressure in the print cartridge. Also, printer throughput and the carriage motion speed may also cause variations in the dynamic ink pressure in the print cartridge. It has been found that, typically, the higher the printer throughput, the greater the range of variation of ink pressure in the cartridge. Similarly, the speed at which the carriage moves will affect the dynamic ink pressure in the print cartridge.